hooks: verify hooks project has worktree before running

Skip hook if its project is not present on disk.

Bug: 434232630
Change-Id: I09a8b412d078af7a068d533f7be320d5b02327be
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/494441
Reviewed-by: Scott Lee <ddoman@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

hooks.py

@@ -101,12 +101,11 @@ class RepoHook:
         self._abort_if_user_denies = abort_if_user_denies
 
         # Store the full path to the script for convenience.
-        if self._hooks_project:
+        self._script_fullpath = None
+        if self._hooks_project and self._hooks_project.worktree:
             self._script_fullpath = os.path.join(
                 self._hooks_project.worktree, self._hook_type + ".py"
             )
-        else:
-            self._script_fullpath = None
 
     def _GetHash(self):
         """Return a hash of the contents of the hooks directory.
@@ -443,6 +442,7 @@ class RepoHook:
         if (
             self._bypass_hooks
             or not self._hooks_project
+            or not self._script_fullpath
             or self._hook_type not in self._hooks_project.enabled_repo_hooks
         ):
             return True